Fuel cell systems are increasingly being used as a power source in a wide variety of applications. Fuel cell systems have been proposed for use in power consumers such as vehicles as a replacement for internal combustion engines, for example. Fuel cells may also be used as stationary electric power plants in buildings and residences, as portable power in video cameras, computers, and the like. Typically, the fuel cells generate electricity used to charge batteries or to provide power for an electric motor.
Fuel cells are electrochemical devices which directly combine a fuel such as hydrogen and an oxidant such as oxygen to produce electricity. The oxygen is typically supplied by an air stream. The hydrogen and oxygen combine to result in the formation of water. Other fuels can be used such as natural gas, methanol, gasoline, and coal-derived synthetic fuels, for example. The term “fuel cell” is typically used to refer to either a single cell or a plurality of cells depending upon the context in which it is used. The plurality of cells is typically bundled together and arranged to form a stack with the plurality of cells commonly arranged in electrical series. Since single fuel cells can be assembled into stacks of varying sizes, systems can be designed to produce a desired energy output level providing flexibility of design for different applications.
Different fuel cell types can be provided such as phosphoric acid, alkaline, molten carbonate, solid oxide, and proton exchange membrane (PEM), for example. The basic components of a PEM-type fuel cell are two electrodes separated by a polymer membrane electrolyte. Each electrode is coated on one side with a thin catalyst layer. The electrodes, catalyst, and membrane together form a membrane electrode assembly (MEA).
In a typical PEM-type fuel cell, the MEA is sandwiched between “anode” and “cathode” diffusion mediums (hereinafter “DM's”) or diffusion layers that are formed from a resilient, conductive, and gas permeable material such as carbon fabric or paper. The DM's serve as the primary current collectors for the anode and cathode as well as provide mechanical support for the MEA. The DM's and MEA, collectively referred to as MEA hereinafter, are pressed between a pair of electronically conductive plates such as bipolar plates, for example, which serve as secondary current collectors for collecting the current from the primary current collectors.
Both of the MEA and the bipolar plate are flexibly thin, approximately less than 1.0 mm, and extremely delicate with special coatings and/or fluid channels. As such, each MEA and bipolar plate is individually packaged with a protective separator to militate against damage thereto during shipping. Accordingly, conventional assembly requires that each MEA and bipolar plate be removed and de-stacked from the individual packages and then re-stacked with either a manual or an automated pick-and-place means. The de-stacking and re-stacking operations, in addition to the delicate nature and limited handling area of the MEA and the bipolar plates, result in a slow assembly process and/or expensive tooling. Furthermore, packing and disposing of the protective separators adds time and cost to the manufacturing cycle.
It would be desirable to develop a modular production method, scalable from a low volume to a high volume production, and produce an apparatus for assembling the MEA and the bipolar plates for a fuel cell stack wherein a cost thereof is minimized and an efficiency thereof is maximized.